Phoronix, known for their various speed tests and reviews, compared the latest in Ubuntu and what, until recently, used to be the lastest in Mac OS X with 29 different benchmarking tests. Some of the results were rather interesting.

It sounds more like you need to upgrade your ram than get a kernel optimized for desktop use. It's not exactly a secret that current mainstream Linux distributions are less memory efficient than XP

I find OS X to be downright viscous -- as though there is perceivable latency between the input devices and the screen. It's possible I'm just imagining things because of the way desktop effects slow down some other actions, but that's how it feels.

I haven't seen that kind of performance since version 10.4.x, even when it's short on available real memory, though I've had stuttering from the virtual memory system when an application tries to implement its own system.

The graphics card has a lot to do with it, though, since OpenGL is used in many places. The early Intel-based machines with the early Intel graphics chipset lagged a lot but then, they weren't able to access 226 MB of shared RAM in Mac OS X the way that they could under Windows.